2019-02-20 18:21:08 -08:00
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use rand::distributions::{Distribution, WeightedIndex};
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use rand::SeedableRng;
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use rand_chacha::ChaChaRng;
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2019-02-19 19:16:27 -08:00
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use solana_sdk::pubkey::Pubkey;
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use std::ops::Index;
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2019-02-24 07:16:13 -08:00
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/// Stake-weighted leader schedule for one epoch.
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2019-04-19 02:39:44 -07:00
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#[derive(Debug, Default, PartialEq)]
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2019-02-19 19:16:27 -08:00
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pub struct LeaderSchedule {
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slot_leaders: Vec<Pubkey>,
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}
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impl LeaderSchedule {
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2019-02-25 06:23:21 -08:00
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// Note: passing in zero stakers will cause a panic.
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2019-03-19 06:36:45 -07:00
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pub fn new(ids_and_stakes: &[(Pubkey, u64)], seed: [u8; 32], len: u64, repeat: u64) -> Self {
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2019-02-25 06:23:21 -08:00
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let (ids, stakes): (Vec<_>, Vec<_>) = ids_and_stakes.iter().cloned().unzip();
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let rng = &mut ChaChaRng::from_seed(seed);
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2019-02-20 18:21:08 -08:00
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let weighted_index = WeightedIndex::new(stakes).unwrap();
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2019-03-19 06:36:45 -07:00
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let mut current_node = Pubkey::default();
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let slot_leaders = (0..len)
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.map(|i| {
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if i % repeat == 0 {
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current_node = ids[weighted_index.sample(rng)];
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current_node
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} else {
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current_node
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}
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})
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.collect();
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2019-02-19 19:16:27 -08:00
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Self { slot_leaders }
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}
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}
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2019-03-14 16:06:56 -07:00
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impl Index<u64> for LeaderSchedule {
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2019-02-19 19:16:27 -08:00
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type Output = Pubkey;
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2019-03-14 16:06:56 -07:00
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fn index(&self, index: u64) -> &Pubkey {
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let index = index as usize;
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2019-02-19 19:16:27 -08:00
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&self.slot_leaders[index % self.slot_leaders.len()]
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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2019-02-20 18:21:08 -08:00
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2019-02-19 19:16:27 -08:00
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#[test]
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fn test_leader_schedule_index() {
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2019-03-30 20:37:33 -07:00
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let pubkey0 = Pubkey::new_rand();
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let pubkey1 = Pubkey::new_rand();
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2019-02-20 18:21:08 -08:00
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let leader_schedule = LeaderSchedule {
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slot_leaders: vec![pubkey0, pubkey1],
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};
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2019-02-19 19:16:27 -08:00
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assert_eq!(leader_schedule[0], pubkey0);
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assert_eq!(leader_schedule[1], pubkey1);
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assert_eq!(leader_schedule[2], pubkey0);
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}
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2019-02-20 18:21:08 -08:00
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#[test]
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2019-02-20 18:49:29 -08:00
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fn test_leader_schedule_basic() {
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2019-02-20 18:21:08 -08:00
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let num_keys = 10;
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2019-03-30 20:37:33 -07:00
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let stakes: Vec<_> = (0..num_keys).map(|i| (Pubkey::new_rand(), i)).collect();
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2019-02-20 18:21:08 -08:00
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2019-03-30 20:37:33 -07:00
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let seed = Pubkey::new_rand();
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2019-02-20 18:21:08 -08:00
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let mut seed_bytes = [0u8; 32];
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seed_bytes.copy_from_slice(seed.as_ref());
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2019-02-20 18:49:29 -08:00
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let len = num_keys * 10;
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2019-03-19 06:36:45 -07:00
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let leader_schedule = LeaderSchedule::new(&stakes, seed_bytes, len, 1);
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let leader_schedule2 = LeaderSchedule::new(&stakes, seed_bytes, len, 1);
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2019-02-20 18:49:29 -08:00
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assert_eq!(leader_schedule.slot_leaders.len() as u64, len);
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2019-02-20 18:21:08 -08:00
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// Check that the same schedule is reproducibly generated
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assert_eq!(leader_schedule, leader_schedule2);
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}
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2019-03-19 06:36:45 -07:00
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#[test]
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fn test_repeated_leader_schedule() {
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let num_keys = 10;
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2019-03-30 20:37:33 -07:00
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let stakes: Vec<_> = (0..num_keys).map(|i| (Pubkey::new_rand(), i)).collect();
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2019-03-19 06:36:45 -07:00
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2019-03-30 20:37:33 -07:00
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let seed = Pubkey::new_rand();
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2019-03-19 06:36:45 -07:00
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let mut seed_bytes = [0u8; 32];
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seed_bytes.copy_from_slice(seed.as_ref());
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let len = num_keys * 10;
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let repeat = 8;
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let leader_schedule = LeaderSchedule::new(&stakes, seed_bytes, len, repeat);
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assert_eq!(leader_schedule.slot_leaders.len() as u64, len);
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let mut leader_node = Pubkey::default();
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for (i, node) in leader_schedule.slot_leaders.iter().enumerate() {
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if i % repeat as usize == 0 {
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leader_node = *node;
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} else {
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assert_eq!(leader_node, *node);
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}
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}
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}
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#[test]
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fn test_repeated_leader_schedule_specific() {
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2019-03-30 20:37:33 -07:00
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let alice_pubkey = Pubkey::new_rand();
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let bob_pubkey = Pubkey::new_rand();
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2019-03-19 06:36:45 -07:00
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let stakes = vec![(alice_pubkey, 2), (bob_pubkey, 1)];
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let seed = Pubkey::default();
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let mut seed_bytes = [0u8; 32];
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seed_bytes.copy_from_slice(seed.as_ref());
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let len = 8;
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// What the schedule looks like without any repeats
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let leaders1 = LeaderSchedule::new(&stakes, seed_bytes, len, 1).slot_leaders;
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// What the schedule looks like with repeats
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let leaders2 = LeaderSchedule::new(&stakes, seed_bytes, len, 2).slot_leaders;
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assert_eq!(leaders1.len(), leaders2.len());
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let leaders1_expected = vec![
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alice_pubkey,
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alice_pubkey,
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alice_pubkey,
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bob_pubkey,
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alice_pubkey,
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alice_pubkey,
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alice_pubkey,
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alice_pubkey,
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];
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let leaders2_expected = vec![
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alice_pubkey,
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alice_pubkey,
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alice_pubkey,
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alice_pubkey,
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alice_pubkey,
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alice_pubkey,
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bob_pubkey,
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bob_pubkey,
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];
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assert_eq!(leaders1, leaders1_expected);
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assert_eq!(leaders2, leaders2_expected);
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}
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2019-02-19 19:16:27 -08:00
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}
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